Use of prospective and retrospective risk assessment methods that simplify chemical mixtures associated with treated domestic wastewater discharges

A framework is presented that is intended to facilitate the evaluation of potential aquatic ecological risks resulting from discharges of down the drain chemicals. A scenario is presented using representatives of many of the types of chemicals that are treated domestically. Predicted treated effluent chemical concentrations (PECS) are based on reported loading rates and routine removal rates for three types of treatment: trickling filter (TF), activated sludge secondary treatment (AS), and AS plus advanced oxidation process (AOP). In Tier I, PECs were compared with the lowest predicted no effect concentration (PNEC) obtained from the literature using safety factors as needed. A cumulative risk characterization ratio (cumRCR) 1.0 for all three treatment types in our scenario, even though no chemical exceeded a hazard quotient of 1.0 in AS or AOP. In Tier 2, AS yielded a lower cumRCR than TF due to higher removal rates and the cumRCR in AOP was <